Protein tyrosine phosphatase 1B inhibitors for diabetes

High-resolution PTP1B inhibition profiling combined with high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy: Proof-of-concept and antidiabetic constituents in crude extract of Eremophila lucida

Type 2 diabetes (T2D) constituted 90% of the global 387 million diabetes cases in 2014. The enzyme protein-tyrosine phosphatase 1B (PTP1B) has been recognized as a therapeutic target for treatment of T2D and its adverse complications. With the aim of accelerating the investigation of complex natural sources, such as crude plant extracts, for potential PTP1B inhibitors, we have developed a bio-analytical platform combining high-resolution PTP1B inhibition profiling and high-performance liquid chromatography-high-resolution mass spectrometry-solid-phase extraction-nuclear magnetic resonance spectroscopy, i.e., HR-bioassay/HPLC-HRMS-SPE-NMR. Human recombinant PTP1B enzyme was used for the microplate-based PTP1B inhibition assay, which was optimized for pH and substrate concentration to be compatible with rate measurements within the 10 min incubation time. Subsequently, analytical-scale HPLC-based microfractionation followed by colorimetric microplate-based PTP1B bioassaying enabled construction of a high-resolution inhibition profile corresponding to the HPLC profile. The high-resolution PTP1B inhibition profiling was validated using an artificial mixture of known PTP1B inhibitors and non-inhibiting compounds as negative controls. Finally, a proof-of-concept study with a real sample was performed using crude ethyl acetate extract of the phytochemically hitherto unexplored plant Eremophila lucida. This led to the identification of the first viscidane type diterpene, i.e., 5-hydroxyviscida-3,14-dien-20-oic acid (9) as PTP1B inhibitor with an IC50 value of 42.0 ± 5.9 μM. In addition, a series of flavonoids, i.e., luteolin (1), dinatin (3a), tricin (3b), 3,6-dimethoxyapigenin (4), jaceidin (5), and cirsimaritin (6) as well as a cembrene diterpene, (3Z, 7E, 11Z)-15-hydroxycembra-3,7,11-trien-19-oic acid (8), were also identified for the first time from E. lucida.

Selective binding modes and allosteric inhibitory effects of lupane triterpenes on protein tyrosine phosphatase 1B

Protein Tyrosine Phosphatase 1B (PTP1B) has been recognized as a promising therapeutic target for treating obesity, diabetes, and certain cancers for over a decade. Previous drug design has focused on inhibitors targeting the active site of PTP1B. However, this has not been successful because the active site is positively charged and conserved among the protein tyrosine phosphatases. Therefore, it is important to develop PTP1B inhibitors with alternative inhibitory strategies. Using computational studies including molecular docking, molecular dynamics simulations, and binding free energy calculations, we found that lupane triterpenes selectively inhibited PTP1B by targeting its more hydrophobic and less conserved allosteric site. These findings were verified using two enzymatic assays. Furthermore, the cell culture studies showed that lupeol and betulinic acid inhibited the PTP1B activity stimulated by TNFα in neurons. Our study indicates that lupane triterpenes are selective PTP1B allosteric inhibitors with significant potential for treating those diseases with elevated PTP1B activity.

Discovery of novel cinnamylidene-thiazolidinedione derivatives as PTP-1B inhibitors for the management of type 2 diabetes

Synthesis, biological evaluation,in silicobinding affinity prediction and 3D-QSAR studies of cinnamylidene-thiazolidinedione derivatives was performed as inhibitors of PTP-1B.

[Low molecular weight regulators of the intracellular insulin signal transduction as a correction method of the insulin resistance in the treatment of type 2 diabetes]

Insulin resistance is the characteristic feature of type 2 diabetes. This condition is manifested in the reduction of peripheral tissues sensitivity to the biological action of insulin and is expressed in the inhibition of cellular glucose absorption and metabolism in response to hormonal stimulation. At the cellular level, disorders which are realized both at the receptor and the postreceptor levels can serve a prerequisite to the formation of insulin resistance and are associated with a change in the amount or dysfunction of major molecular signaling cascade. Thus, the insulin receptor, as well as the other related signaling molecules can be considered as ideal therapeutic targets for the correction of insulin resistance and thus low molecular weight effectors which act on the individual links of insulin signaling cascade may be positioned as a new generation of anti-diabetic agents. This report provides information on the regulators of insulin receptor cascade, main advantages and disadvantages of their impact on biological targets and prospects for their therapeutic use as anti-diabetic drugs.

Molecular docking assisted 3D-QSAR study of benzylidene-2,4-thiazolidinedione derivatives as PTP-1B inhibitors for the management of Type-2 diabetes mellitus

An integrated molecular docking assisted 3D-QSAR study was performed on benzylidene-2,4-thiazolidinediones to identify spatial fingerprints for designing PTP-1B inhibitors.

Hypoglycemic effect and mechanism of honokiol on type 2 diabetic mice

BACKGROUND

Honokiol is one of the main bioactive constituents of the traditional Chinese herbal drug Magnolia bark (Cortex Magnoliae officinalis, Hou Po). The aim of this study was to probe its anti-type 2 diabetes mellitus effects and the underlying mechanism.

METHODS

Type 2 diabetic mouse model was established by intraperitoneally injecting with streptozotocin. Fasting blood glucose, body weight, and lipid profile were measured. The subcutaneous adipose tissue, skeletal muscle, and liver were isolated as well as homogenized. The phospho-insulin receptor β-subunit (IRβ), IRβ, phospho-AKT, AKT, phospho-ERK1/2, ERK1/2, phosphotyrosine, and actin were examined by Western blot assay. Cell viability or cytotoxicity was analyzed by using MTT method. The inhibitory potencies of honokiol on the protein tyrosine phosphatase 1B (PTP1B) activity were performed in reaction buffer. Molecular docking and dynamic simulation were also analyzed.

RESULTS

In in vivo studies, oral treatment with 200 mg/kg honokiol for 8 weeks significantly decreases the fasting blood glucose in type 2 diabetes mellitus mice. The phosphorylations of the IRβ and the downstream insulin signaling factors including AKT and ERK1/2 significantly increase in adipose, skeletal muscle, and liver tissue of the honokiol-treated mice. Moreover, honokiol enhanced the insulin-stimulated phosphorylations of IRβ, AKT, and ERK1/2 in a dose-dependent manner in C2C12 myotube cells. Meanwhile, honokiol enhanced insulin-stimulated GLUT4 translocation. Importantly, honokiol exhibited reversible competitive inhibitory activity against PTP1B with good selectivity in vitro and in vivo. Furthermore, using molecular docking and dynamic simulation approaches, we determined the potential binding mode of honokiol to PTP1B at an atomic level.

CONCLUSION

These findings indicated the hypoglycemic effects of honokiol and its mechanism that honokiol improved the insulin sensitivity by targeting PTP1B. Therefore, our study may highlight honokiol as a promising insulin sensitizer for the therapy of type 2 diabetes.

Reactions of 1,3-Diketones with a Dipeptide Isothiazolidin-3-one: Toward Agents That Covalently Capture Oxidized Protein Tyrosine Phosphatase 1B

Protein tyrosine phosphatase 1B (PTP1B) is a validated therapeutic target for the treatment of type 2 diabetes; however, the enzyme has been classified by some as an "undruggable target". Here we describe studies directed toward the development of agents that covalently capture the sulfenyl amide "oxoform" of PTP1B generated during insulin signaling events. The sulfenyl amide residue found in oxidized PTP1B presents a unique electrophilic sulfur center that may be exploited in drug and probe design. Covalent capture of oxidized PTP1B could permanently disable the intracellular pool of enzyme involved in regulation of insulin signaling. Here, we employed a dipeptide model of oxidized PTP1B to investigate the nucleophilic capture of the sulfenyl amide residue by structurally diverse 1,3-diketones. All of the 1,3-diketones examined here reacted readily with the electrophilic sulfur center in the sulfenyl amide residue to generate stable covalent attachments. Several different types of products were observed, depending upon the substituents present on the 1,3-diketone. The results provide a chemical foundation for the development of agents that covalently capture the oxidized form of PTP1B generated in cells during insulin signaling events.

Chlorabietols A-C, Phloroglucinol-Diterpene Adducts from the Chloranthaceae Plant Chloranthus oldhamii

Three unprecedented phloroglucinol-diterpene adducts, chlorabietols A-C (1-3), were isolated from the roots of the rare Chloranthaceae plant Chloranthus oldhamii. They represent a new class of compounds, featuring an abietane-type diterpenoid coupled with different alkenyl phloroglucinol units by forming a 2,3-dihydrofuran ring. Their structures were elucidated by detailed spectroscopic analysis, molecular modeling studies, and electronic circular dichroism calculations. Compounds 1-3 showed inhibitory activity against protein tyrosine phosphatase 1B (PTP1B) with IC50 values of 12.6, 5.3, and 4.9 μM, respectively.

Identification of Bidentate Salicylic Acid Inhibitors of PTP1B

PTP1B is a master regulator in the insulin and leptin metabolic pathways. Hyper-activated PTP1B results in insulin resistance and is viewed as a key factor in the onset of type II diabetes and obesity. Moreover, inhibition of PTP1B expression in cancer cells dramatically inhibits cell growth in vitro and in vivo. Herein, we report the computationally guided optimization of a salicylic acid-based PTP1B inhibitor 6, identifying new and more potent bidentate PTP1B inhibitors, such as 20h, which exhibited a > 4-fold improvement in activity. In CHO-IR cells, 20f, 20h, and 20j suppressed PTP1B activity and restored insulin receptor phosphorylation levels. Notably, 20f, which displayed a 5-fold selectivity for PTP1B over the closely related PTPσ protein, showed no inhibition of PTP-LAR, PRL2 A/S, MKPX, or papain. Finally, 20i and 20j displayed nanomolar inhibition of PTPσ, representing interesting lead compounds for further investigation.

Protein tyrosine phosphatase 1B inhibitory activity of alkaloids from Rhizoma Coptidis and their molecular docking studies

ETHNOPHARMACOLOGIC RELEVANCE

Rhizoma Coptidis (the rhizome of Coptis chinensis Franch) has commonly been used for treatment of diabetes mellitus in traditional Chinese medicine due to its blood sugar-lowering properties and therapeutic benefits which highly related to the alkaloids therein. However, a limited number of studies focused on the Coptis alkaloids other than berberine.

MATERIALS AND METHODS

In the present study, we investigated the anti-diabetic potential of Coptis alkaloids, including berberine (1), epiberberine (2), magnoflorine (3), and coptisine (4), by evaluating the ability of these compounds to inhibit protein tyrosine phosphatase 1B (PTP1B), and ONOO(-)-mediated protein tyrosine nitration. We scrutinized the potentials of Coptis alkaloids as PTP1B inhibitors via enzyme kinetics and molecular docking simulation.

RESULTS

The Coptis alkaloids 1-4 exhibited remarkable inhibitory activities against PTP1B with the IC50 values of 16.43, 24.19, 28.14, and 51.04 μM, respectively, when compared to the positive control ursolic acid. These alkaloids also suppressed ONOO(-)-mediated tyrosine nitration effectively in a dose dependent manner. In addition, our kinetic study using the Lineweaver-Burk and Dixon plots revealed that 1 and 2 showed a mixed-type inhibition against PTP1B, while 3 and 4 noncompetitively inhibited PTP1B. Moreover, molecular docking simulation of these compounds demonstrated negative binding energies (Autodock 4.0=-6.7 to -7.8 kcal/mol; Fred 2.0=-59.4 to -68.2 kcal/mol) and a high proximity to PTP1B residues, including Phe182 and Asp181 in the WPD loop, Cys215 in the active sites and Tyr46, Arg47, Asp48, Val49, Ser216, Ala217, Gly218, Ile219, Gly220, Arg221 and Gln262 in the pocket site, indicating a higher affinity and tighter binding capacity of these alkaloids for the active site of the enzyme.

CONCLUSION

Our results clearly indicate the promising anti-diabetic potential of Coptis alkaloids as inhibitors on PTP1B as well as suppressors of ONOO(-)-mediated protein tyrosine nitration, and thus hold promise as therapeutic agents for the treatment of diabetes and related disease.

Marine Bromophenol Derivative 3,4-Dibromo-5-(2-bromo-3,4-dihydroxy-6-isopropoxymethyl benzyl)benzene-1,2-diol Protects Hepatocytes from Lipid-Induced Cell Damage and Insulin Resistance via PTP1B Inhibition

3,4-Dibromo-5-(2-bromo-3,4-dihydroxy-6-isopropoxymethyl benzyl)benzene-1,2-diol (HPN) is a bromophenol derivative from the marine red alga Rhodomela confervoides. We have previously found that HPN exerted an anti-hyperglycemic property in db/db mouse model. In the present study, we found that HPN could protect HepG2 cells against palmitate (PA)-induced cell death. Data also showed that HPN inhibited cell death mainly by blocking the cell apoptosis. Further studies demonstrated that HPN (especially at 1.0 μM) significantly restored insulin-stimulated tyrosine phosphorylation of IR and IRS1/2, and inhibited the PTP1B expression level in HepG2 cells. Furthermore, the expression of Akt was activated by HPN, and glucose uptake was significantly increased in PA-treated HepG2 cells. Our results suggest that HPN could protect hepatocytes from lipid-induced cell damage and insulin resistance via PTP1B inhibition. Thus, HPN can be considered to have potential for the development of anti-diabetic agent that could protect both hepatic cell mass and function.

Crystal structures of the apo form and a complex of human LMW-PTP with a phosphonic acid provide new evidence of a secondary site potentially related to the anchorage of natural substrates

Low molecular weight protein tyrosine phosphatases (LMW-PTP, EC 3.1.3.48) are a family of single-domain enzymes with molecular weight up to 18 kDa, expressed in different tissues and considered attractive pharmacological targets for cancer chemotherapy. Despite this, few LMW-PTP inhibitors have been described to date, and the structural information on LMW-PTP druggable binding sites is scarce. In this study, a small series of phosphonic acids were designed based on a new crystallographic structure of LMW-PTP complexed with benzylsulfonic acid, determined at 2.1Å. In silico docking was used as a tool to interpret the structural and enzyme kinetics data, as well as to design new analogs. From the synthesized series, two compounds were found to act as competitive inhibitors, with inhibition constants of 0.124 and 0.047 mM. We also report the 2.4Å structure of another complex in which LMW-PTP is bound to benzylphosphonic acid, and a structure of apo LMW-PTP determined at 2.3Å resolution. Although no appreciable conformation changes were observed, in the latter structures, amino acid residues from an expression tag were found bound to a hydrophobic region at the protein surface. This regions is neighbored by positively charged residues, adjacent to the active site pocket, suggesting that this region might be not a mere artefact of crystal contacts but an indication of a possible anchoring region for the natural substrate-which is a phosphorylated protein.

Accessing biological actions of Ganoderma secondary metabolites by in silico profiling

The species complex around the medicinal fungus Ganoderma lucidum Karst. (Ganodermataceae) is widely known in traditional medicines, as well as in modern applications such as functional food or nutraceuticals. A considerable number of publications reflects its abundance and variety in biological actions either provoked by primary metabolites, such as polysaccharides, or secondary metabolites, such as lanostane-type triterpenes. However, due to this remarkable amount of information, a rationalization of the individual Ganoderma constituents to biological actions on a molecular level is quite challenging. To overcome this issue, a database was generated containing meta-information, i.e., chemical structures and biological actions of hitherto identified Ganoderma constituents (279). This was followed by a computational approach subjecting this 3D multi-conformational molecular dataset to in silico parallel screening against an in-house collection of validated structure- and ligand-based 3D pharmacophore models. The predictive power of the evaluated in silico tools and hints from traditional application fields served as criteria for the model selection. Thus, the focus was laid on representative druggable targets in the field of viral infections (5) and diseases related to the metabolic syndrome (22). The results obtained from this in silico approach were compared to bioactivity data available from the literature. 89 and 197 Ganoderma compounds were predicted as ligands of at least one of the selected pharmacological targets in the antiviral and the metabolic syndrome screening, respectively. Among them only a minority of individual compounds (around 10%) has ever been investigated on these targets or for the associated biological activity. Accordingly, this study discloses putative ligand target interactions for a plethora of Ganoderma constituents in the empirically manifested field of viral diseases and metabolic syndrome which serve as a basis for future applications to access yet undiscovered biological actions of Ganoderma secondary metabolites on a molecular level.

Hypoglycemic Effect of the Methanol flower Extract of Piper Claussenianum and the Major Constituent 2',6'-dihydroxy-4'-methoxychalcone in Streptozotocin Diabetic Rats

Piper claussenianum inflorescences crude methanol extract was tested for hypoglycemic effect in streptozotocin-induced diabetic rats. The blood glucose levels of rats treated with methanol extract were reduced from 318.4±28.1 mg/dl before treatment to 174.2±38.3 mg/dl after 12 days of treatment (P<0.05). Phytochemical studies were carried out on inflorescences methanol crude extract in order to investigate the possible metabolites responsible for the pharmacological properties of the extract. After chromatographic procedures, three flavonoids were isolated and characterized. The major compound 2’,6’-dihydroxy-4’-methoxychalcone was also tested. Rats that received the chalcone content also displayed a reduction in blood glucose levels from 277.4±7.7 mg/dl before treatment to 158.8±9.2 mg/dl after 12 days of treatment (P<0.05). The results suggest this chalcone is one of the metabolite responsible for the blood glucose levels reduction in rats with streptozotocin-induced diabetes. The inflorescence crude extract of P. claussenianum was found to be composed mainly by flavonoids and may be a potential natural source of compounds with hypoglycemic properties.

Design and synthesis of novel 1,2-dithiolan-4-yl benzoate derivatives as PTP1B inhibitors

A series of novel 1,2-dithiolan-4-yl benzoate compounds were synthesized and evaluated for in vitro PTP1B inhibitory activity. Some derivatives exhibited improved PTP1B inhibitory activity and selectivity compared to hit 6a, a compound from in-house library screening inspired by marine cyclic disulfide. The preliminary SAR analysis with assistance of molecular modeling approach revealed 6j (IC50=0.59μM) as the most potent PTP1B inhibitor among all derivatives.

Novel stilbenes from Artocarpus nanchuanensis

Four new stilbene derivatives, hypargystilbenes B-E (1-4), together with seven known compounds (5-11), were isolated from the stems of Artocarpus nanchuanensis S.S. Chang. Their structures were elucidated on the basis of spectral data. Hypargystilbene B, hypargystilbene D, and hypargystilbene E exhibited protein tyrosine phosphatase 1B inhibitory effects with corresponding IC50 values of 3.23, 37.31, and 2.53 nM.

Diabetes and Alzheimer disease, two overlapping pathologies with the same background: oxidative stress

There are several oxidative stress-related pathways interconnecting Alzheimer's disease and type II diabetes, two public health problems worldwide. Coincidences are so compelling that it is attractive to speculate they are the same disorder. However, some pathological mechanisms as observed in diabetes are not necessarily the same mechanisms related to Alzheimer's or the only ones related to Alzheimer's pathology. Oxidative stress is inherent to Alzheimer's and feeds a vicious cycle with other key pathological features, such as inflammation and Ca²⁺ dysregulation. Alzheimer's pathology by itself may lead to insulin resistance in brain, insulin resistance being an intervening variable in the neurodegenerative disorder. Hyperglycemia and insulin resistance from diabetes, overlapping with the Alzheimer's pathology, aggravate the progression of the neurodegenerative processes, indeed. But the same pathophysiological background is behind the consequences, oxidative stress. We emphasize oxidative stress and its detrimental role in some key regulatory enzymes.

Binding cavities and druggability of intrinsically disordered proteins

To assess the potential of intrinsically disordered proteins (IDPs) as drug design targets, we have analyzed the ligand-binding cavities of two datasets of IDPs (containing 37 and 16 entries, respectively) and compared their properties with those of conventional ordered (folded) proteins. IDPs were predicted to possess more binding cavity than ordered proteins at similar length, supporting the proposed advantage of IDPs economizing genome and protein resources. The cavity number has a wide distribution within each conformation ensemble for IDPs. The geometries of the cavities of IDPs differ from the cavities of ordered proteins, for example, the cavities of IDPs have larger surface areas and volumes, and are more likely to be composed of a single segment. The druggability of the cavities was examined, and the average druggable probability is estimated to be 9% for IDPs, which is almost twice that for ordered proteins (5%). Some IDPs with druggable cavities that are associated with diseases are listed. The optimism versus obstacles for drug design for IDPs is also briefly discussed.

Insulin-mimetic selaginellins from Selaginella tamariscina with protein tyrosine phosphatase 1B (PTP1B) inhibitory activity

As part of an ongoing search for new antidiabetic agents from medicinal plants, three new (2, 4, and 5) and two known selaginellin derivatives (1 and 3) were isolated from a methanol extract of Selaginella tamariscina. The structures of the new compounds were determined by spectroscopic data analysis. All isolates showed strong glucose uptake stimulatory effects in 3T3-L1 adipocyte cells at a concentration of 5 μM. Furthermore, these compounds were found to possess inhibitory effects on PTP1B enzyme activity with IC50 values ranging from 4.6 ± 0.1 to 21.6 ± 1.5 μM. Compound 2 showed the greatest potency, with an IC50 value of 4.6 ± 0.1 μM, when compared with the positive control (ursolic acid, IC50 = 3.5 ± 0.1 μM). Therefore, these selaginellin derivatives may have value as new lead compounds for the development of agents against type 2 diabetes.

Enantiomeric 3-arylcoumarins and 2-arylcoumarones from the roots of Glycyrrhiza uralensis as protein tyrosine phosphatase 1B (PTP1B) inhibitors

Four new PTP1B inhibitors were isolated from Glycyrrhiza uralensis, and the absolute configuration of 2,3-dihydro-2,3,3-trimethylbenzofurans was first unambiguously established.

Novel heteroaryl phosphonicdiamides PTPs inhibitors as anti-hyperglycemic agents

BACKGROUND

Chronic and oral administration of benzylamine improves glucose tolerance. Picolylamine is a selective functional antagonist of the human adenosine A2B receptor. Phosphonic diamide derivatives enhance the cellular permeability and in turn their biological activities.

METHODS

A series of heteroaryl phosphonicdiamide derivatives were designed as therapeutics to control and manage type2 diabetes. Initially defined Lipinski parameters encouraged them as safer drugs. Molecular docking of these compounds against Protein tyrosine phosphatase (PTP), the potential therapeutic target of type 2 diabetes, revealed their potential binding ability explaining their anti-diabetic activity in terms of PTP inhibition. Human intestinal absorption, Caco-2 cell permeability, MDCK cell permeability, BBB penetration, skin permeability and plasma protein binding abilities of the title compounds were calculated by PreADMET server. A convenient method has been developed for the synthesis of title compounds through the formation of 1-ethoxy-N,N'-bis(4-fluorobenzyl/pyridin-3-ylmethyl)phosphinediamine by the reaction of 4-fluorobenzylamine/ 3-picolylamine with ethyldichlorophosphite, subsequently reacted with heteroaryl halides using lanthanum(III) chloride as a catalyst.

RESULTS

All the compounds exhibited significant in vitro anti-oxidant activity and in vivo evaluation in streptozotocin induced diabetic rat models revealed that the normal glycemic levels were observed on 12(th) day by 9a and 20(th) day by 5b, 5c, 9e and 9f. The remaining compounds also exhibited normal glycemic levels by 25(th) day.

CONCLUSION

The results from molecular modeling, in vitro and in vivo studies are suggesting them as safer and effective therapeutic agents against type2 diabetes. Graphical Abstract Development of PTPs inhibitors.

Role of physical exercise on hepatic insulin, glucocorticoid and inflammatory signaling pathways in an animal model of non-alcoholic steatohepatitis

AIMS

Pro-inflammatory mediators, glucocorticoids and transforming growth factor (TGF)-β are implicated in the pathogenesis of non-alcoholic steatohepatitis (NASH)-related insulin resistance. As physical activity is beneficial against NASH, we analyzed the voluntary physical activity (VPA) and endurance training (ET) (preventive and therapeutic strategies) effects on hepatic insulin, pro-inflammatory and glucocorticoid signaling regulators/mediators in high-fat (Lieber-DeCarli) diet (HFD)-induced NASH.

MAIN METHODS

Adult male Sprague-Dawley rats were divided in standard diet (SD) or HFD, with sedentary, VPA and ET animals in both diet regimens. Plasma glucose and insulin concentrations were analyzed; plasma insulin sensitivity index (ISI) was calculated. Hepatic insulin, pro-inflammatory and glucocorticoid signaling regulators/mediators were evaluated by Western blot or reverse transcriptase-PCR.

KEY FINDINGS

ET improved ISI in both diet regimens. HFD-feeding increased interleukin-1β and induced a similar pattern on interleukin-6 and TGF-β, which were globally reduced by physical exercise. ET decreased HFD leukemia inhibitory factor level, SD+VPA animals presenting higher values than HFD+VPA animals. HFD increased the ratio of IRS-1(Ser307)/total IRS-1, which was completely mitigated by physical exercise. Physical exercise reduced total ERK and JNK (total and activated) expression in HFD. In SD vs. HFD, VPA presented higher activated JNK and ET presented higher total JNK. Generally, in HFD, the ratio (activated/total) of AKT, and each separately, decreased with exercise and also for activated AKT in SD. Overall, in both diets, exercise reduced 11β-hydroxysteroid dehydrogenase type 1. ET increased glucocorticoid receptor and reduced PTP1B in HFD.

SIGNIFICANCE

Physical exercise mitigates the expression of pro-inflammatory mediators and positively modulates insulin and glucocorticoid signaling in NASH.

The second-sphere residue T263 is important for the function and catalytic activity of PTP1B via interaction with the WPD-loop

Protein tyrosine phosphatases have diverse substrate specificities and intrinsic activities that lay the foundations for the fine-tuning of a phosphorylation network to precisely regulate cellular signal transduction. All classical PTPs share common catalytic mechanisms, and the important catalytic residues in the first sphere of their active sites have been well characterized. However, little attention has been paid to the second-sphere residues that are potentially important in defining the intrinsic activity and substrate specificity of PTPs. Here, we find that a conserved second-sphere residue, Thr263, located in the surface Q-loop is important for both the function and activity of PTPs. Using PTP1B as a study model, we found that mutations of Thr263 impaired the negative regulation role of PTP1B in insulin signaling. A detailed mechanistic study utilizing steady-state kinetics, Brønsted analysis and pH dependence in the presence of pNPP or phosphopeptide substrates revealed that Thr263 is required for the stabilization of the leaving group during catalysis. Further crystallographic studies and structural comparison revealed that Thr263 regulates the general acid function through modulation of the WPD-loop by the T263:F182/Y/H interaction pair, which is conserved in 26 out of 32 classical PTPs. In addition, the hydrophobic interaction between Thr263 and Arg1159 of the insulin receptor contributes to the substrate specificity of PTP1B. Taken together, our findings demonstrate the general role of the second-sphere residue Thr263 in PTP catalysis. Our findings suggest that the second sphere residues of PTP active site may play important roles in PTP-mediated function in both normal and diseased states.

Effect of Hypericum perforatum L. extract on insulin resistance and lipid metabolic disorder in high-fat-diet induced obese mice

Natural product Hypericum perforatum L. has been used in folk medicine to improve mental performance. However, the effect of H. perforatum L. on metabolism is still unknown. In order to test whether H. perforatum L. extract (EHP) has an effect on metabolic syndrome, we treated diet induced obese (DIO) C57BL/6J mice with the extract. The chemical characters of EHP were investigated with thin-layer chromatography, ultraviolet, high-performance liquid chromatography (HPLC), and HPLC-mass spectrometry fingerprint analysis. Oral glucose tolerance test (OGTT), insulin tolerance test (ITT), and the glucose infusion rate (GIR) in hyperinsulinemic–euglycemic clamp test were performed to evaluate the glucose metabolism and insulin sensitivity. Skeletal muscle was examined for lipid metabolism. The results suggest that EHP can significantly improve the glucose and lipid metabolism in DIO mice. In vitro, EHP inhibited the catalytic activity of recombinant human protein tyrosine phosphatase 1B (PTP1B) and reduced the protein and mRNA levels of PTP1B in the skeletal muscle. Moreover, expressions of genes related to fatty acid uptake and oxidation were changed by EHP in the skeletal muscle. These results suggest that EHP may improve insulin resistance and lipid metabolism in DIO mice. © 2014 The Authors. Phytotherapy Research published by John Wiley & Sons Ltd.

Synthesis of oleanolic acid derivatives: In vitro, in vivo and in silico studies for PTP-1B inhibition

Non-insulin dependent diabetes mellitus is a multifactorial disease that links different metabolic routes; a point of convergence is the enzyme PTP-1B which turns off insulin and leptin receptors involved in glucose and lipid metabolism, respectively. Pentacyclic acid triterpenes such as oleanolic acid (OA) have proved to be excellent PTP-1B inhibitors, thus, the purpose of current work was to generate a series of derivatives that improve the pharmacological effect of OA. Our findings suggest that the presence of the carboxylic acid and/or its corresponding reduction product carbinol derivative (H-bond donor) in C-28 is required to maintain the inhibitory activity; moreover, this is further enhanced by ester or ether formation on C-3. The most active derivatives were cinnamoyl ester (6) and ethyl ether (10). Compound 6 showed potent in vitro inhibitory activity and significantly decrease of blood glucose levels on in vivo experiments. Meanwhile, 10 showed contrasting outcomes, since it was the compound with higher inhibitory activity and selectivity over PTP-1B and has improved interaction with site B, according with docking studies, the in vivo antidiabetic effect was similar to oleanolic acid. In conclusion, oleanolic acid derivatives have revealed an enhanced inhibitory effect over PTP-1B activity by increasing molecular interactions with either catalytic or allosteric sites and producing a hypoglycaemic effect on non insulin dependent diabetes mellitus rat model.

PTP1B inhibitors for type 2 diabetes treatment: a patent review (2011 - 2014)

INTRODUCTION

Protein tyrosine phosphatase 1B (PTP1B) plays an important role in the negative regulation of insulin signal transduction pathway and has emerged as novel therapeutic strategy for the treatment of type 2 diabetes. PTP1B inhibitors enhance the sensibility of insulin receptor (IR) and have favorable curing effect for insulin resistance-related diseases. A large number of PTP1B inhibitors, either synthetic or isolated as bioactive agents from natural products, have developed and investigated for their ability to stimulate insulin signaling.

AREAS COVERED

This review includes an updated summary (2011 - 2014) of PTP1B inhibitors that have been published in patent applications, with an emphasis on their chemical structure, mode of action and therapeutic outcomes. The usefulness of PTP1B inhibitors as pharmaceutical agents for the treatment of type 2 diabetes is also discussed.

EXPERT OPINION

PTP1B inhibitors show beneficial effects to enhance sensibility of IR by restricting the activity of enzyme and have favorable curing effects. However, structural homologies in the catalytic domain of PTP1B with other protein tyrosine phosphatases (PTPs) like leukocyte common antigen-related, CD45, SHP-2 and T-cell-PTP present a challenging task of achieving selectivity. Thus, for therapeutic application of PTP1B inhibitors, highly selective molecules exhibiting desired effects without side effects are expected to find clinical application.

Novel and emerging diabetes mellitus drug therapies for the type 2 diabetes patient

Type 2 diabetes mellitus is a metabolic disorder of deranged fat, protein and carbohydrate metabolism resulting in hyperglycemia as a result of insulin resistance and inadequate insulin secretion. Although a wide variety of diabetes therapies is available, yet limited efficacy, adverse effects, cost, contraindications, renal dosage adjustments, inflexible dosing schedules and weight gain significantly limit their use. In addition, many patients in the United States fail to meet the therapeutic HbA1c goal of < 7% set by the American Diabetes Association. As such new and emerging diabetes therapies with different mechanisms of action hope to address some of these drawbacks to improve the patient with type 2 diabetes. This article reviews new and emerging classes, including the sodium-glucose cotransporter-2 inhibitors, 11β-Hydroxysteroid dehydrogenase type 1 inhibitors, glycogen phosphorylase inhibitors; protein tyrosine phosphatase 1B inhibitors, G Protein-Coupled receptor agonists and glucokinase activators. These emerging diabetes agents hold the promise of providing benefit of glucose lowering, weight reduction, low hypoglycemia risk, improve insulin sensitivity, pancreatic β cell preservation, and oral formulation availability. However, further studies are needed to evaluate their safety profile, cardiovascular effects, and efficacy durability in order to determine their role in type 2 diabetes management.

Investigating the impact of Asp181 point mutations on interactions between PTP1B and phosphotyrosine substrate

Protein tyrosine phosphatase 1B (PTP1B) is a key negative regulator of insulin and leptin signaling, which suggests that it is an attractive therapeutic target in type II diabetes and obesity. The aim of this research is to explore residues which interact with phosphotyrosine substrate can be affected by D181 point mutations and lead to increased substrate binding. To achieve this goal, molecular dynamics simulations were performed on wild type (WT) and two mutated PTP1B/substrate complexes. The cross-correlation and principal component analyses show that point mutations can affect the motions of some residues in the active site of PTP1B. Moreover, the hydrogen bond and energy decomposition analyses indicate that apart from residue 181, point mutations have influence on the interactions of substrate with several residues in the active site of PTP1B.

Bidentate inhibitors of protein tyrosine phosphatases

SIGNIFICANCE

Protein tyrosine phosphatases (PTPs) are important enzymes that are involved in the regulation of cellular signaling. Evidence accumulated over the years has indicated that PTPs present exciting opportunities for drug discovery against diseases such as diabetes, cancer, autoimmune diseases, and tuberculosis. However, the highly conserved and partially positive charge of the catalytic sites of PTPs is a major challenge in the development of potent and highly selective PTP inhibitors.

RECENT ADVANCES

Here, we examine the strategy of developing bidentate inhibitors for selective inhibition of PTPs. Bidentate inhibitors are small-molecular-weight compounds with the ability to bind to both the active site and a non-conserved secondary phosphate binding site. This secondary phosphate binding site was initially discovered in protein tyrosine phosphatase 1B (PTP1B), and, hence, most of the bidentate inhibitors reported in this review are PTP1B inhibitors.

CRITICAL ISSUES

Although bidentate inhibition is a good strategy for developing potent and selective inhibitors, the cell membrane permeability and pharmacokinetic properties of the inhibitors are also important for successful drug development. In this review, we will also summarize the various efforts made toward the development of phosphotyrosine (pTyr) mimetics for increasing cellular permeability.

FUTURE DIRECTIONS

Even though the secondary phosphate binding site was initially found in PTP1B, structural data have shown that a secondary binding site can also be found in other PTPs, albeit with varying degrees of accessibility. Along with improvements in pTyr mimetics, we believe that the future will see an increase in the number of orally bioavailable bidentate inhibitors against the various classes of PTPs.

The prelude on novel receptor and ligand targets involved in the treatment of diabetes mellitus

Metabolic disorders are a group of disorders, due to the disruption of the normal metabolic process at a cellular level. Diabetes Mellitus and Tyrosinaemia are the majorly reported metabolic disorders. Among them, Diabetes Mellitus is a one of the leading metabolic syndrome, affecting 5 to 7 % of the population worldwide and mainly characterised by elevated levels of glucose and is associated with two types of physiological event disturbances such as impaired insulin secretion and insulin resistance. Up to now, various treatment strategies are like insulin, alphaglucosidase inhibitors, biguanides, incretins were being followed. Concurrently, various novel therapeutic strategies are required to advance the therapy of Diabetes mellitus. For the last few decades, there has been an extensive research in understanding the metabolic pathways involved in Diabetes Mellitus at the cellular level and having the profound knowledge on cell-growth, cell-cycle, and apoptosis at a molecular level provides new targets for the treatment of Diabetes Mellitus. Receptor signalling has been involved in these mechanisms, to translate the information coming from outside. To understand the various receptors involved in these pathways, we must have a sound knowledge on receptors and ligands involved in it. This review mainly summarises the receptors and ligands which are involved the Diabetes Mellitus. Finally, researchers have to develop the alternative chemical moieties that retain their affinity to receptors and efficacy. Diabetes Mellitus being a metabolic disorder due to the glucose surfeit, demands the need for regular exercise along with dietary changes.

Screening assay for small-molecule inhibitors of synaptojanin 1, a synaptic phosphoinositide phosphatase

Elevation of amyloid β-peptide (Aβ) is critically associated with Alzheimer disease (AD) pathogenesis. Aβ-induced synaptic abnormalities, including altered receptor trafficking and synapse loss, have been linked to cognitive deficits in AD. Recent work implicates a lipid critical for neuronal function, phosphatidylinositol-4,5-bisphosphate [PI(4,5)P2], in Aβ-induced synaptic and behavioral impairments. Synaptojanin 1 (Synj1), a lipid phosphatase mediating the breakdown of PI(4,5)P2, has been shown to play a role in synaptic vesicle recycling and receptor trafficking in neurons. Heterozygous deletion of Synj1 protected neurons from Aβ-induced synaptic loss and restored learning and memory in a mouse model of AD. Thus, inhibition of Synj1 may ameliorate Aβ-associated impairments, suggesting Synj1 as a potential therapeutic target. To this end, we developed a screening assay for Synj1 based on detection of inorganic phosphate liberation from a water-soluble, short-chain PI(4,5)P2. The assay displayed saturable kinetics and detected Synj1's substrate preference for PI(4,5)P2 over PI(3,4,5)P3. The assay will enable identification of novel Synj1 inhibitors that have potential utility as chemical probes to dissect the cellular role of Synj1 as well as potential to prevent or reverse AD-associated synaptic abnormalities.

Efficient immobilization of the enzyme and substrate for a single-step caspase-3 inhibitor assay using a combinable PDMS capillary sensor array

Caspase-3 inhibitor assay was successfully integrated into “single-step” by solving the problem of low-activity enzyme immobilization by using a combinable poly(dimethylsiloxane) capillary (CPC) sensor.